1. Field of the Invention
The invention relates to a post processing method and apparatus for generating a scrolling waveform display from an existing erase bar waveform display. More particularly, the invention relates to a device and post processing method for reversibly converting an electrocardiograph system (ECG) with an existing erase bar waveform display to one with a scrolling waveform display.
2. Description of the Prior Art
Doctors often have to make critical split second decisions while treating patients. To facilitate the clinical decision making process hospitals and clinics are equipped with a myriad of biomedical devices. One such device is the ubiquitous ECG. The ECG monitors and displays a patient's vital signs. Although the information that the ECG provides is extremely valuable many clinicians have indicated a dissatisfaction with the manner in which this information is displayed by the ECG display unit and thereby communicated to them.
The current ECG display procedure, with which many clinicians are dissatisfied, involves an "erase bar." As soon as the ECG is turned on the display unit screen displays a waveform (each pulse representing a heartbeat) which begins on the left most side of the display unit screen and proceeds towards the right side of the display unit screen. Once the waveform reaches the right most side of the display unit screen (such that the waveform extends from the right most side of screen to the left most side of the screen) an erase bar, moving from left to right and starting on the left most side of the screen, begins to erase the waveform. The erase bar typically has a leading edge facing the right side of the display unit screen and a trailing edge facing the left hand side of the screen. As the oldest data points of the first waveform are being erased on the leading edge of the erase bar, new data points are displayed on the trailing edge of the erase bar thus forming a new waveform.
Use of the erase bar display method for displaying ECG waveforms has two main drawbacks. First, the erase bar method forces the user to follow the trailing edge of the erase bar in order to see how the waveform is changing. If a clinician wants to read the ECG output waveform he or she must spend precious time: (1)first locating the erase bar on the display unit screen; and (2)then shifting his or her eyes to the left of the erase bar (the trailing edge) to see the new waveform being displayed. The second main drawback of the erase bar display method relates to individual heartbeat comparisons. In order to compare the two most recent individual heart beat pulses using the erase bar display method a clinician must: (1)isolate the erase bar on the display unit screen; (2)look to the left of the erase bar (the trailing edge) and locate the most recent pulse; and (3)compare this pulse to the second most recent pulse, which could be at the right most side of the display unit screen (since the erase bar moves across the screen). This process is not only time consuming but is also error prone. This is especially so if several waveforms are displayed simultaneously, each moving at different rates, forcing the erase bars to be unsynchronized (displayed in different locations).
A scrolling waveform display method eliminates the above mentioned drawbacks of the erase bar display method. In a scrolling waveform display the most current waveform information is fixed at one location (usually the right most portion of the display unit screen). The waveform flows from right to left without the presence of a distracting erase bar. The entire continuous waveform scrolls to the left, erasing the oldest data point on the left most portion of the display unit screen on a frame-by-frame basis, and allowing the newest data point to be drawn on the right most portion of the display unit screen. In order to compare the two most recent heartbeat pulses one simply has to recognize that the waveform is continuous and that all of the heartbeat pulses are ordered time wise. The earliest heartbeat pulse is displayed furthest left on the display unit screen and the most recent heartbeat pulse is displayed furthest right on the display unit screen.
Several methods have been used to generate a scrolling waveform display in the past. One such method, involves hardware that shifts memory address locations. For example, consider a memory unit that has four memory locations: location 1, location 2, location 3, and location 4. Data in each memory location indicates whether a certain pixel on the ECG display screen should be on or off (assuming a black and white display). Assume that the screen only has four pixels: pixel 1, pixel 2, pixel 3, and pixel 4. Data in location 1 controls pixel 1. Similarly, data in locations 2,3, and 4 control pixels 2,3, and 4, respectively. Data is first stored in each memory location. Next, the data is displayed on the ECG screen. In order to create a scrolling effect, before a new data point can be stored in memory, the data in location two must be shifted to location one and the data in location 3 must be shifted to location 3. Once this shifting is completed, the new data can be store in location 4. Now that the memory has been refreshed with the updated data, the data can be displayed on the screen. Since the newest data is always stored in location 4, which controls pixel 4, the newest data point will always appear on the right most side of the display screen, thus creating a scrolling waveform.
U.S. Pat. No. 5,289,575, by Nakagawa and Nojima, discloses a video display system for vertically scrolling text in selected portions of a display. The video display system disclosed employs the memory address shifting method discussed above to create scrolling.
A disadvantage with the above mentioned method involves variable scroll rates. Specialized display hardware can be designed to accomplish memory address shifting, however, as a result of the design of the hardware required to produce scrolling (shifting data in memory locations) there can only be one scroll rate. If there are three different waveforms being displayed on the display screen they must all scroll at the same rates. Furthermore, the entire screen must scroll. This is a problem for an ECG display unit where it is desired that only the waveforms scroll and not the vital sign numbers. The reason that there is only one scroll rate is because the data displayed on the display screen all comes from a single memory unit, which can only have one shift rate (rate of shifting data between adjacent memory locations).
High end scrolling waveform displays overcome this problem by having more than one memory unit. Waveforms are made to scroll at different rates by changing the shift rates of each individual memory unit. This technique is widely used in computer type applications. U.S. Pat. No. 4,873,514, for example, by Godfrey, discloses a hardware system having two memory units so as to allow for a single portion of the display to scroll while the rest of the display remains stationary. A disadvantage of this solution, however, is that it requires specialized and costly hardware: multiple memory units, commonly referred to as video planes (one for each simultaneous scrolling speed, including the static background).
A second method used to generate a scrolling waveform involves real time animation software. Such software basically redraws the entire waveform on a frame by frame basis. Every time a new data point is collected the data displayed by each pixel must be recalculated and restored. Implementing this method, therefore, requires a great deal of extra processing, and as a result, is very expensive.
While these methods may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.